Migrate documentation theme to PyData Sphinx theme

[Copilot]

This PR migrates the documentation theme from the Read the Docs theme to the modern PyData Sphinx theme, providing a cleaner and more consistent appearance with other PyData ecosystem projects.

Changes Made

• Updated dependencies: Replaced sphinx-rtd-theme with pydata-sphinx-theme>=0.13.0 in pyproject.toml
• Updated Sphinx configuration: Changed html_theme from "sphinx_rtd_theme" to "pydata_sphinx_theme" in docs/source/conf.py
• Added theme configuration: Integrated GitHub repository links and edit page buttons for better user experience
• Updated ReadTheDocs config: Migrated from Poetry to UV build system in .readthedocs.yaml to match project tooling

Theme Features

The new PyData Sphinx theme provides:

• Modern, responsive design with better mobile support
• GitHub integration with direct links to edit documentation pages
• Consistent styling with other PyData projects (pandas, NumPy, matplotlib, etc.)
• Better accessibility and navigation

Testing

• ✅ Documentation builds successfully with new theme
• ✅ All existing tests continue to pass
• ✅ Theme renders correctly with proper styling and navigation
• ✅ GitHub integration works as expected

The migration maintains all existing documentation content while providing a more modern and user-friendly interface.

Fixes #311.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.